I am often asked why there isn't any written information on how to do low-fire-salt
fuming. Despite the fact that it has been practiced for more than 20 years,
I don't know of any books or articles giving specific directions. The following
are concepts and methods I have learned mostly through trial and error.

In the beginning, it should be expected that there will be even more accidental
effects from low-fire salting than ever found in raku. Perhaps this is the reason
that so little information is available. Nevertheless, with experience accumulated
from each firing, potters can discover what works best in their own kilns. And,
yes, soda can also be fumed in the same way as salt.

The Clay Body

Almost any clay can be used in low-fire-salt fuming, but if orange-flashing
effects are desired, then the body should include some iron oxide. If slips,
terra sigillata or stains are to be applied to the surface, the clay body can
be any stoneware, porcelain or a raku blend.

My favorite low-fire-salt body is a mixture of equal parts plastic fireclay,
Kentucky ball clay (OM 4), red clay and sand (20 to 60 mesh). Note that there
is an absence of flux; however, salt vapor fluxes the body, making it harder
than regular bisqueware even at Cone 010.

The Kiln

Either an updraft or downdraft fuel-burning kiln can be used. Excellent results
can be obtained with hardbrick, softbrick, even fiber kilns, but the burner
ports must enter horizontally. Kilns with bottom burners cannot be used because
salt cannot be volatilized anywhere in the kiln except in the burner flame itself.

A salting port should be located directly above each burner so that salt can
be dropped into the flame. Because it is important that salt fall into the flame,
each burner port should be no higher than the kiln floor. If it is higher, build
a salting platform level with each burner. The kiln also needs a peephole near
the bottom of the door so that the quality of the atmosphere can be inspected
during the firing. Finally, there must be a primary-air control on each burner.

Stacking

Effects of low-fire salting can be compared to high-temperature wood firings.
Variation is enhanced by the flame moving through the ware; there is also a
flame-resist effect when work is tightly stacked and touching. In some ways,
flame movement is similar to the beautiful patterns produced by a river flowing
under, over and through rocks. In this case, the flame is the river and the
pots are the rocks.

Specific patterns can be achieved by masking surfaces with thin (approximately
1/8-inch-thick) pancakes of clay. Several layers of pages from glossy magazines
or even thin slices of wood if placed under a clay pancake will produce dark
gray patterns. Keep in mind that the shapes of the masking objects that touch
the surfaces will have an effect on the patterns they leave.

Other patterns can be achieved by embedding rock salt into the clay pancake.
A few large grains of salt will leave a beauty spot! Metal oxides or organic
materials like seaweed can also be used.

The kiln, properly stacked for low-fire-salt fuming, will look like a disaster
area to the uniformed observer. And it will necessarily be completely full.
Shelves are not only unecessary, but actually nonproductive, as glazes are not
used and the temperature is so low.

Surface Preparation

If there is a small amount of iron in the clay body, spectacular oranges, yellows
and brown flashing can be expected. Raku slips will also have a positive reaction
to the process. A raku white slip containing 1 part Gerstley borate, 2 parts
flint and 3 parts kaolin will often flash a beautiful pink from copper added
to the salt or fumed off other copper-decorated ware. The same slip with 3%-5%
copper carbonate added will be even more reactive.

Colors (from copper in particular) are often quite varied because of the complex
stacking, which results in reduction-oxidation and neutral flames licking over
the object simultaneously. Similar variation in flashing can be anticipated
from the use of terra sigillatas; however, the sigillata should be applied very
thinly and/or fired to a higher temperature (possibly from Cone 06 to Cone 01)
to prevent cracking. Applying the sigillata to damp bisqueware also seems to
help. Remember, less planned decoration is better, and none is often good enough.

Firing

The firing cycle is approximately the same length as a bisque firing. Although
stacking, surface preparation and body composition are important, it is the
quality and the quantity of the flame that make low-fire-salt fuming so different
from other firings. To begin, the primary air on each burner is reduced to make
a long, dirty, soft yellow flame for the entire firing. Oxidation and reduction
cycles of glaze firings are of little significance in the low-fire salting;
however, to pull the flame through the ware, dampers need to be open throughout
the entire firing.

Of utmost importance is the need to fire the kiln with excess fuel. This is
determined by observing the pressure at the bottom peephole. Above 1300 degrees
Fahrenheit, visible flames should be exiting constantly from the peephole. If
this state cannot be maintained, increase the gas, add extra burners or drill
out the burner orifices until flames are obtained.

Of course, this is a reducing atmosphere, except that it is achieved with the
dampers opened and the kiln drawing. Curiously, cones will change their melting
point and are therefore not an exact indication of the actual temperature, but
are close enough to warrant their use.

Salting

Before loading the kiln, place salt in the flame path of each burner. A mound
the size of a large orange is a good amount to start with.

When the kiln turns dull red, at about 1000 degrees Fahrenheit, add more salt
to each burner. For convenience, the salt can be wrapped in newspaper to form
a salt "burrito," then pushed through the salting port into the flame. Additional
salting every hour should be enough to achieve the desired effects.

A small amount of copper carbonate added to the salt may be helpful in encouraging
a pink blush on the otherwise white slip surfaces. Many other oxides may be
used to modify the fuming effects, but none as dramatically.

Oversalting may dull the surface color, so be conservative. Salting at the
end of the firing is optional. Personal experience will determine its importance
or not. Also, experiment with closing the dampers during the salting cycle,
but only for a few minutes.

Work decorated with slips can be fired from Cone 010 to Cone 06. Terra-sigillata
surfaces are better fired higher, from Cone 08 to Cone 3. Because there is no
glaze to melt, precise temperature control is not a problem.

After the cones have melted and the last salt burrito has been added, the kiln
can be shut off and cooled in the usual manner; no other treatment is needed
or helpful. A good rule is to cool the kiln in the same amount of time it took
to fire it.

Postfiring

In order to protect the somewhat soft surfaces, apply one or two coats of acrylic
floor wax (such as Futura) diluted about half and half with water to both the
inside and out. If the result is too shiny when dry, dilute the wax a little
more. The coating will preserve the colors and allow the work to be cleaned
by washing with water from time to time.